This invention relates to a motor drive circuit for driving an electromotor with a permanent magnet rotor and a stator comprising one or more stator windings, the motor drive circuit comprising an excitation circuit for exciting the stator windings, a signal generation circuit for generating an emergency control signal which indicates a failure of the excitation of the stator windings, and an auxiliary power supply circuit for extracting electric energy from the motor in response to the emergency control signal and supplying the extracted energy to an auxiliary circuit, the auxiliary power supply circuit comprising a rectifier circuit inserted between at least one stator winding and the auxiliary circuit.
The invention further relates to a data reading and/or recording apparatus comprising a motor for driving in a rotating fashion a disc having a recording layer, a read/write head arranged opposite the recording layer and movable in a radial direction relative to the disc, an actuator for moving the head and a positioning control means for energizing the actuator, and a motor drive circuit as defined in the opening paragraph. The positioning control means is coupled to the auxiliary power supply circuit for its energy supply. The positioning control means is arranged to cause the magnetic head to be moved to an idle position in response to the emergency control signal.
A motor drive circuit of this type as well as data read and/or recording (apparatus in the form of a so-called magnetic hard disc drive are known, for example, from U.S. Pat No. 4,371,903.
The use of a motor drive circuit of the type defined in the opening paragraph is especially interesting for use with magnetic hard disc drives. With these hard disc drives an air cushion is developed between the read/write head and the disc as a result of the high speed of rotation of the disc, thus avoiding mechanical contact between the head and the disc. If the drive motor is de-energized as a result of a power failure, the r.p.m. of the motor and thus the speed of rotation of the disc is reduced. In order to prevent the head from contacting the disc when the motor is de-energized, the head is moved to an idle position by an electrically driven actuator before the disc speed has dropped below the critical value. The required electric power is extracted from the drive motor which is used as a generator in the case of a power failure.
Generally, the motor drive circuit and the logic circuits preferably have the same supply voltage. For reducing heat dissipation in the logic circuits, low voltages of the order of several volts are preferably chosen for the power supply of the logic circuits. If the motor used is also designed for these low voltages, the problem will occur that the voltage generated by the motor while acting as a generator is too low for the actuator to be energized for moving the head because the generated voltage is only several volts. The useful voltage, however, is even considerably less as a result of the relatively large voltage drop across the diodes included in the rectifier circuit. It is an object of the invention to provide a motor drive circuit by which electric energy having a considerably higher voltage level can be extracted from the motor once the motor has been de-energized.